I am almost certain that "cocoa with skin" refers to the skin that forms on the surface of boiled milk. See https://en.wikipedia.org/wiki/Milk_skin . Cocoa is a dry powder made from chocolate. It is different from chocolate because it has had most of the fat removed. Cocoa is also the name of the chocolate-flavored hot drink, made by mixing cocoa powder, sugar, and hot milk. Since it's made from hot milk, a skin can form on it. When I was a kid, I hated the skin, as many children do. Now that I am grown up, I still hate it. The skin only forms if the milk is brought to the boiling point. Some people try to avoid it by making cocoa with very warm milk that is not hot enough to form a skin. My mother allowed me to pick the skin off and drop it in the saucer, without eating it. Unfortunately, in many traditions, the skin is thought to be very healthy. (It is concentrated protein). Therefore, it is not unusual for parents to insist on kids eating (bleagh! augh! ick! yuck!) the milk skin. If I understand correctly, the parents want him to drink the cocoa because they think it's healthy, and whenever he does they reward him. They give him a bigger reward if he eats the skin. The story is told in the "voice" of a child. The flow of phrases and ideas is like that of a child. Therefore it is somewhat hard to understand.

The only skin on cocoa that I know of is the slightly tough, almost membrane like hardened surface that forms on top when the cocoa cools significantly